1. Field of the Invention
The present invention relates to positive temperature coefficient heaters, and, more particularly, to positive temperature coefficient heaters which may be exposed to high voltage spikes or surges.
2. Description of the Related Art
A positive temperature coefficient (PTC) heater includes a semi-conductive body with an electrical resistance which varies as a function of temperature. Electrical conductors are typically attached to opposite surfaces of the body and an electrical current is passed through the body during use. The electrical current passing through the body causes the temperature of the body to rise. As the temperature of the body rises, the electrical resistance of the body also increases.
A PTC heater may occasionally be exposed to high voltage spikes or surges during use. The PTC heater is typically not protected from the high voltage spikes and surges. The semi-conductive electrical properties of the body of the PTC heater may not allow the electrical current associated with the voltage spike to pass therethrough in a sufficient manner with respect to time. As a result, an electrical potential may develop between the electrical conductors at the opposing surfaces of the body which in turn may result in the formation of an electric field at the input side of the body. The electric field may result in arcing around the periphery of the PTC heater, rendering the surface of the PTC heater conductive because of carbonization by the arc flame. In the course of arcing, the PTC heater may suffer cracking or pitting, or may become brittle due to the heat of the arcing.
Devices are known which cut off power to or limit power through a PTC heater when it has reached a certain temperature to prevent damage to the PTC heater from excessive heat. But these devices are designed to protect the PTC heater in the normal household voltage operating range. These devices are not designed to protect the PTC heater from voltage spikes or surges in the kilovolt range, and the devices cannot react quickly enough to do so.
What is needed in the art is a way to protect the PTC heater from damage from high voltage spikes or surges.